Networks having multiple paths between nodes and nodes for such a network

ABSTRACT

A method of operating a network that contains a plurality of nodes is disclosed. The plurality of nodes include a first node and a second node with the first and second nodes being connected via a first path and a second path that are different. The method includes operating the network in first and second modes of operation. In the first mode, traffic between the first and second nodes is transmitted over the first path and not the second path. In the second mode, traffic is transmitted over the first and second paths. The mode of operation is selected based upon a level of traffic between the first and second nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International ApplicationPCT/EP2007/061774 with an international filing date of 31 Oct. 2007,which corresponds to the national-stage entry U.S. application Ser. No.12/680,450, filed 1 Nov. 2010, the disclosures of which are incorporatedherein by reference.

TECHNICAL FIELD

This invention relates to a network, a network node, and a method ofoperating a network, in which at least two paths are provided betweentwo nodes of the network.

BACKGROUND

Network communication is well known. In a network, it is often desiredto transmit traffic from a source node to a destination node across thenetwork. To ensure the reliability of communication between such pairsof nodes, it is known to provide protection for communication channels.

In such a scheme, a primary connection through the network isestablished. A protection connection is also established taking adifferent path through the network. The protection connection is not, innormal use used. It only comes into action should the primary connectionfail due to loss of signal, loss of continuity, increased error rate,dropped frames or so on.

A single protection connection may be dedicated to a particular primaryconnection (1:1 protection) or may be shared between multiple primaryconnections (1:n protection) depending upon how important it is that agiven connection is maintained. Such protection schemes are described inthe International Telecommunications Union (ITU) recommendations numbersG.808.1 and G841, the disclosures of which are hereby incorporated byreference.

SUMMARY

According to a first aspect of the invention, there is provided anetwork comprising a plurality of nodes, the plurality of nodescomprising a first node and a second node, the first and second nodesbeing connected through the network of nodes via first path and a secondpath, the first and second paths being different, in which the networkhas first and second modes of operation, a first mode in which trafficbetween the first and second nodes is transmitted over the first pathand not the second path, and a second mode where the traffic istransmitted over the first and second paths, wherein the networkcomprises a mode selector arranged to select the mode of operation basedupon a demanded level of traffic between the first and second nodes.

Accordingly, this can be seen as primarily using the first path totransmit data over, but only using the second path should that becomenecessary. In a particularly advantageous embodiment, the second pathcomprises a protection path such that the network has a third mode ofoperation in which traffic between the first and second nodes is sentover only the second path, and in which the mode selector is arranged toselect this mode should there be a fault on the first path. By thesemeans, known protection paths which would otherwise be idle can be usedwhilst there is not a fault, but be brought into play should a faultarise.

The first and second paths may be different; they may traverse differentsets of intermediate nodes through the network. This is typical inprotection paths.

The selection of the mode of operation dependent upon the demanded levelof traffic may depend upon the rate at which data to be transmittedacross the link is received. For example, a simple calculation of therate at which data for the link are received could be employed. The modeselector may therefore comprise comparison means to compare the ratewith a threshold; if the rate exceeds the threshold then the second modeof operation may be selected. The threshold may be a fraction of anavailable bandwidth of the first path, such as 80% or 100%,

The network may further comprise a priority assignor, which is operableto assign a priority to the assignment of data between the first andsecond paths. Where the second path comprises a protection path, datafor the protection path that is potentially to be routed onto the secondpath because of a failure in the network may have a higher priority thanthat assigned to data potentially to be assigned to the second pathbecause of traffic levels. The first node is preferably arranged toassign data to the first or second paths dependent upon the priorityassigned to the data.

According to a second aspect of the invention, there is provided anetwork node for use in sending data to a destination node in a network,the network node comprising a first network interface and a secondnetwork interface, in which the network node has first and second modesof operation, a first mode in which the network node transmits data forthe destination using the first network interface and not the secondnetwork interface, and a second mode where the data for the destinationnode is transmitted over the first and second network interfaces,wherein the network node comprises a mode selector arranged to selectthe mode of operation based upon a demanded level of traffic for thedestination node.

Again, this allows a secondary path to be selected should the trafficbetween the network node and the destination node require it. Typically,in use, the first network interface would be connected to a first pathacross the network to the destination node and the second networkinterface would be connected to a second path across the network to thedestination node.

The network node may comprise a protection switch, whereby in case of afault traffic for the destination node is sent via the second networkinterface should there be a fault on a link from the first interface tothe destination node. In a particularly advantageous embodiment, thesecond path comprises a protection path such that the second mode ofoperation is selected should there be a fault in the first path. Bythese means, known protection paths which would otherwise be idle can beused whilst there is not a fault, but be brought into play should afault arise.

The first and second paths may he different; they may traverse differentsets of intermediate nodes through the network. This is typical inprotection paths.

The selection of the mode of operation dependent upon the demanded levelof traffic may depend upon the rate at which data to be transmittedacross the link is received. For example, a simple calculation of therate at which data for the link are received could be employed. The modeselector may therefore comprise comparison means to compare the ratewith a threshold; if the rate exceeds the threshold then the second modeof operation may be selected. The threshold may be a fraction of anavailable bandwidth of the first path, such as 80% or 1.00%.

The network may further comprise a priority assignor, which is operableto assign a priority to the assignment of data between the first andsecond paths. Where the second path comprises a protection path, datafor the protection path that is potentially to be routed onto the secondpath because of a failure in the network may have a higher priority thanthat assigned to data potentially assigned to the second path because oftraffic levels. The first node is preferably arranged to assign data tothe first or second paths dependent upon the priority assigned to thedata.

According to a third aspect of the invention, there is provided a methodof operating a network, the network comprising a plurality of nodes, theplurality of nodes comprising a first node and a second node, the firstand second nodes being connected through the network of nodes via firstpath and a second path, the first and second paths being different,

the method comprising the operation of the network in first and secondmodes of operation, a first mode in which traffic between the first andsecond nodes is transmitted over the first path and not the second path,and a second mode where the traffic is transmitted over the first andsecond paths, and wherein the mode of operation is selected based upon alevel of traffic between the first and second nodes.

Accordingly, this can be seen as primarily using the first path totransmit data over, but only using the second path should that becomenecessary. In a particularly advantageous embodiment, the second pathcomprises a protection path such that the network is operated in a thirdmode of operation in which traffic between the first and second nodes issent over only the second path, and in which the third mode is selectedshould there be a fault on the first path. By these means, knownprotection paths which would otherwise be idle can be used whilst thereis not a fault, but be brought into play should a fault arise.

The first and second paths may be different; they may traverse differentsets of intermediate nodes through the network. This is typical inprotection paths.

The selection of the mode of operation dependent upon the demanded levelof traffic may depend upon the rate at which data to be transmittedacross the link is received. For example, a simple calculation of therate at which data for the link are received could be employed. The modeselector may therefore comprise comparison means to compare the ratewith a threshold; if the rate exceeds the threshold then the second modeof operation may be selected. The threshold may be a fraction of anavailable bandwidth of the first path, such as 80% or 100%.

The method may comprise the step of assigning a priority to theassignment of data between the first and second paths. Where the secondpath comprises a protection path, data for the protection path that ispotentially to be routed onto the second path because of a failure inthe network may have a higher priority than that assigned to datapotentially assigned to the second path because of traffic levels. Datais preferably assigned to the first or second paths dependent upon thepriority assigned to the data.

According to a fourth aspect of the invention, there is provided amethod of operating a network node so as to send data to a destinationnode in a network, the network node comprising a first network interfaceand a second network interface, in which the method comprises operatingthe network node in first and second modes of operation: a first mode inwhich the network node transmits data for the destination using thefirst network interface and not the second network interface, and asecond mode where the data for the destination node is transmitted overthe first and second network interfaces, and wherein the mode isselected based upon a level of traffic for the destination node.

Again, this allows a secondary path to be selected should the trafficbetween the network node and the destination node require it. Typically,in use, the first network interface would be connected to a first pathacross the network to the destination node and the second networkinterface would be connected to a second path across the network to thedestination node.

The network node may comprise a protection switch, whereby in case of afault traffic for the destination node is sent via the second networkinterface should there be a fault on a link from the first interface tothe destination node. In a particularly advantageous embodiment, thesecond path comprises a protection path such that the second mode ofoperation is selected should there be a fault in the first path. Bythese means, known protection paths which would otherwise be idle can beused whilst there is not a fault, but be brought into play should afault arise.

The first and second paths may be different; they may traverse differentsets of intermediate nodes through the network. This is typical inprotection paths.

The selection of the mode of operation dependent upon the demanded levelof traffic may depend upon the rate at which data to be transmittedacross the link is received. For example, a simple calculation of therate at which data for the link are received could be employed. The modeselector may therefore comprise comparison means to compare the ratewith a threshold; if the rate exceeds the threshold then the second modeof operation may be selected. The threshold may be a fraction of anavailable bandwidth of the first path, such, as 80% or 100%.

The method may further comprise the assignment of a priority to theassignment of data between the first and second paths. Where the secondpath comprises a protection path, data for the protection path that ispotentially to be routed onto the second path because of a failure inthe network may have a higher priority than that assigned to datapotentially assigned to the second path because of traffic levels. Thefirst node is preferably arranged to assign data to the first or secondpaths dependent upon the priority assigned to the data.

Any of the nodes of any of the aspects of the invention may comprise aplurality of interfaces and associated equipment. The interfaces of thenode may comprise both customer or network-facing interfaces, and thenetwork interfaces referred to above may refer to any or all of suchinterfaces. Such interfaces may represent ingress or egress interfacesinto or from the network. The interfaces may also be connected tofurther networks, for network interconnection.

The behaviour of the mode selector, or the selection of a mode may becontrollable from a network management device, which may be locatedremote to the network node. Such network management device may bearranged to selectively disable the operation of the second mode, sothat the operator of a network can cause the network, node or method torevert to the operation of prior art protection circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematic view of a network according to an embodiment ofthe invention; and

FIG. 2 shows a flow chart showing how data is assigned to the differentlinks of FIG. 1.

DETAILED DESCRIPTION

A network according to an embodiment of the invention is shown in FIG. 1of the accompanying drawings. This comprises two network nodes A and Bconnected via network 1. The nodes are connected by two paths, primarypath 2 and secondary path 3. Each path 2, 3 comprises a plurality ofintermediate nodes 4; the two paths 2, 3 are different in that theytraverse different intermediate nodes. The primary path starts at aprimary network interface 5 of node A and terminates at a primarynetwork interface 6 of node B, whereas the secondary path starts at asecondary network interface 7 of node A and terminates at secondarynetwork interface 8 of node B.

The nodes A and B may be connected by any of the following protocols:SDH/SONET, Ethernet, MPLS, or any packet based transmission protocol.

In a known network configuration, communication traffic for node B (as adestination node) from node A (as a source node) would generally be sentover the primary path 2 unless a fault developed on that path (forexample if one of the intermediate nodes 4 or one of the primary networkinterfaces stopped functioning). In such a case, the traffic would besent over secondary path 3 instead. In such a case the secondary pathcould be considered to be a protection path.

However, this embodiment of the invention relies upon the fact that, formost of the time, the secondary path will be unused and so represents anunderutilisation of bandwidth. Accordingly, the secondary path is usedonce the bitrate of the traffic for node B at node A increases over athreshold. This makes use of the secondary path when there is not afault, utilising otherwise unused bandwidth. This may be achieved bycounting the number of data delivered to the primary network interface 5at node A, and once a threshold is crossed, switching the data to thesecondary path 3.

In order to ensure that a reasonable resiliency is still maintained, ahigh priority is assigned to protection against certain equipment (nodesor interfaces) having defects. Accordingly, the priority with which datais switched from the primary path 2 to the secondary path 3 may be setlower than if the primary path 2 were to fail. Such a priority may beimplemented in line with an Automatic Protection Switching protocol suchas are set out in ITU recommendations G.808.1 and G841. Such priority isnot necessarily required in such a simple embodiment as that shown inFIG. 1 of the accompanying drawings, but the skilled man will appreciateits necessity in larger networks.

Accordingly, the assignment of data between the differing connectionscan be demonstrated as illustrated in FIG. 2 of the accompanyingdrawings. When data is received at node A for node B, software runningon a processor 10 within node A will assign data to the primary orsecondary links 2, 3 using the method shown. The first step 100 is todetermine whether the primary link is functioning correctly. If it isnot, then all data will be sent by the secondary link at step 102. Ifthe primary link is functioning, then the software determines at step104 whether the bitrate of the data from node A for node B is greaterthan a threshold. If it is, then at step 106 both links will be used,whereas if not then only the primary link is used at step 108.

1. A network comprising a plurality of nodes, the plurality of nodescomprising a first node and a second node, the first and second nodesbeing connected through the network of nodes via a first path and asecond path, the first and second paths being different, in which thenetwork has first and second modes of operation, a first mode in whichtraffic between the first and second nodes is transmitted over the firstpath and not the second path, and a second mode where the traffic istransmitted over the first and second paths, wherein the networkcomprises a mode selector arranged to select the mode of operation basedupon a demanded level of traffic between the first and second nodes. 2.The network of claim 1, in which the second path comprises a protectionpath such that the network has a third mode of operation in whichtraffic between the first and second nodes is sent over only the secondpath, and in which the mode selector is arranged to select this modeshould there be a fault on the first path.
 3. The network of claim 1, inwhich the selection of the mode of operation dependent upon the demandedlevel of traffic depends upon the rate at which data to be transmittedacross the link is received.
 4. The network of claim 1, in which thenetwork former comprises a priority assignor, which is operable toassign a priority to the assignment of data between the first and secondpaths.
 5. A network node for use in sending data to a destination nodein a network, the network node comprising a first network interface anda second network interlace, in which the network node has first andsecond modes of operation, a first mode m which the network nodetransmits data for the destination using the first network interface andnot the second network interface, and a second mode where the data forthe destination node is transmitted over the first and second networkinterfaces, wherein the network node comprises a mode selector arrangedto select the mode of operation based upon a demanded level of trafficfor the destination node.
 6. The network node of claim 5, in which thefirst network interface is connectable to a first path across thenetwork to the destination node and the second network interlace isconnectable to a second path across the network to the destination node.7. The network node of claim 5, in which the network node comprises aprotection switch, whereby in case of a fault traffic for thedestination node is sent via the second network interface should therebe a fault on a link from the first interface to the destination node.8. The network node of claim 5, in which the selection of the mode ofoperation dependent upon the demanded level of traffic depends upon therate at which data to be transmitted across the link is received.
 9. Thenetwork node of claim 5, in which the network node further comprises apriority assignor, which is operable to assign a priority to theassignment of data between the first and second paths.
 10. A method ofoperating a network, the network comprising a plurality of nodes, theplurality of nodes comprising a first node and a second node, the firstand second nodes being connected through the network of nodes via afirst path and a second path, the first and second paths beingdifferent, the method comprising the operation of the network in firstand second modes of operation, a first mode in which traffic between thefirst and second nodes is transmitted over the first path and not thesecond path, and a second mode where the traffic is transmitted over thefirst and second paths, and wherein the mode of operation, is selectedbased upon a level of traffic between the first and second nodes. 11.The method of claim 10, in which the second path comprises a protectionpath such that the network is operated in a third mode of operation inwhich traffic between the first and second nodes is sent over only thesecond path, and in which the third mode is selected should there be afault on the first path.
 12. The method of claim 10, in which theselection of the mode of operation dependent upon the demanded level oftraffic depends upon the rate at which data to be transmitted across thelink is received.
 13. The method of claim 12 in which the selection ismade dependent upon whether the rate exceeds a threshold.
 14. The methodof claim 13, in which the threshold is a fraction of an availablebandwidth of the first path.
 15. The method of claim 10, in which themethod comprises the step of assigning a priority to the assignment ofdata between the first and second paths.
 16. The method of claim 15, inwhich data that is potentially to be routed onto the second path becauseof a failure in the network is assigned a higher priority than thatassigned to data potentially to be assigned to the second path becauseof traffic levels.
 17. A method of operating a network node so as tosend data to a destination node in a network, the network nodecomprising a first network interlace and a second network interface, inwhich the method comprises operating the network node in first andsecond modes of operation: a first mode in which the network nodetransmits data for the destination using the first network interface andnot the second network interface, and a second mode where the data forthe destination node is transmuted over the first and second networkinterfaces, and wherein the mode is selected based upon a level oftraffic for the destination node.